Azo compound and liquid crystal composition containing the same

ABSTRACT

A novel azo compound, which has a high dichroic ratio as well as a high solubility in liquid crystals, and a liquid crystal composition containing the same as disclosed. The liquid crystal composition enables an excellent and clear color display.

FIELD OF THE INVENTION

This invention relates to a novel azo compound and a liquid crystal composition containing said compound.

BACKGROUND OF THE INVENTION

There has been known a color display device wherein a liquid crystal composition in which a dyestuff compound is dissolved in liquid crystals is located between two electrodes so as to utilize the guest/host effect of said dyestuff compound and liquid crystals.

A dyestuff compound to be used in such a liquid crystal composition as described above should have a particularly high dichroic ratio as well as a high solubility in liquid crystals.

However we have found that conventional azo compounds do not always satisfy these requirements as a dyestuff compound to be used in a liquid crystal composition.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an azo compound which has a high dichroic ratio and a high solubility in liquid crystals as well as a liquid crystal composition which enables an excellent color display.

Under these circumstances, we have attempted to extend the molecular chain of an azo dyestuff in the longer direction via acetylene bonds. As a result, we have found a dyestuff having a particularly high dichroic ratio and a high solubility, thus completing the present invention.

Accordingly, the present invention provides an azo compound of the following general formula (I): ##STR1## wherein R¹ represents an alkyl group or a ##STR2## group (wherein R³ represents an alkyl group); ##STR3## represent each ##STR4## group optionally sugstituted with an alkyl group or a halogen atom, ##STR5## m and n are each 0 or 1; R² represents a --OR³, ##STR6## (wherein R³ is as defined above and R⁴ represents a hydrogen atom or an alkyl group), ##STR7## (wherein R⁵ represents a hydrogen atom or an alkyl group and R⁶ represents a hydrogen atom or an alkyl or alkoxy group), ##STR8## group; and an alkyl substituent in ##STR9## may bound to an alkyl group R³, R⁴ or R⁵ in ##STR10## of the R² group to thereby form a nitrogen-containing aliphatic ring; and a liquid crystal composition containing said compound.

DETAILED DESCRIPTION OF THE INVENTION

Examples of the alkyl groups in R¹, R³, R⁴, R⁵ and R⁶ in the azo compound of the general formula (I) of the present invention include those carrying 1 to 16 carbon atoms, preferably 1 to 10 carbon atoms. Examples of the alkoxy group in R⁶ include those carrying one to ten carbon atoms.

Examples of the halogen atoms in the optionally substituted ##STR11## include chlorine and fluorine atoms, while examples of the alkyl group therein include lower alkyl groups such as methyl and ethyl groups. Examples of the alkyl-substituted phenyl group include ##STR12## Examples of the nitrogen-containing aliphatic ring wherein the alkyl substituent in the ##STR13## is bound to an alkyl group R³, R⁴ or R⁵ in ##STR14## of the R² group include ##STR15##

m and n represent each 0 or 1. The compound of the general formula (I) comprises, for example, the following monoazo compound, disazo compound or trisazo compound. ##STR16## wherein R¹, R², ##STR17## are as defined in the above general formula (I).

In the compound of the general formula (II), the substituent ##STR18## preferably represents a ##STR19## group; the substituent ##STR20## preferably represents a ##STR21## group; the substituent ##STR22## preferably represents a ##STR23## group; and the substituent ##STR24## preferably represents a ##STR25## optionally substituted with a methyl group or a fluorine atom or ##STR26## group. The R' preferably represents an alkyl, ##STR27## group wherein R³ represents an alkyl group. The group R² preferably represents an ##STR28## wherein R³ and R⁴ represent each an alkyl group or an ##STR29## wherein R⁶ represents an alkyl or alkoxy group. It is further preferable that the ##STR30## R¹ and R² represent each the preferable group as cited above. When R² is an ##STR31## group, it is preferable, from the viewpoint of solubility, that R⁶ is an alkyl group.

In the disazo compound of the general formula (III), the substituent ##STR32## preferably represents a ##STR33## group optionally substituted with an alkyl group; the substituent ##STR34## preferably represents a ##STR35## group optionally substituted with an alkyl group; the substituent ##STR36## preferably represents a ##STR37## group optionally substituted with an alkyl group; R¹ preferably represents an alkyl, ##STR38## group (wherein R³ represents an alkyl group); and R² preferably represents a ##STR39## (wherein R³ and R⁴ represent each an alkyl group) or ##STR40## group (wherein R⁶ represents a hydrogen atom or an alkyl or alkoxy group).

The disazo compound of the general formula (III) may be roughly classified into the following three types (1), (2) and (3) depending on various factors including readiness of the preparation, availability of starting materials, tone, light-resistance, order parameter and color density.

(1) A compound of the general formula (III) wherein ##STR41## group optionally substituted with an alkyl group; ##STR42## group optionally substituted with an alkyl group; ##STR43## group optionally substituted with an alkyl group; R¹ is an alkyl, ##STR44## group (wherein R³ is an alkyl group); R² is an ##STR45## (wherein R³ and R⁴ represent each an alkyl group) or ##STR46## group (wherein R⁶ represents a hydrogen atom or an alkyl or alkoxy group). It is particularly preferable that ##STR47## group optionally substituted with an alkyl group; R¹ is a ##STR48## group (R³ is an alkyl group); and R² is an ##STR49## (wherein R³ and R⁴ represent each an alkyl group) or ##STR50## group (wherein R⁶ is an alkyl or alkoxy group).

(2) A compound of the general formula (III) wherein ##STR51## and R¹ are as defined in (1); while R² represents a ##STR52## group (wherein R³ is an alkyl group). It is particularly preferable that ##STR53## group optionally substituted with an alkyl group; R¹ is a ##STR54## group (wherein R³ is an alkyl group); and R² is a ##STR55## group (wherein R³ is an alkyl group).

(3) A compound of the general formula (III)

wherein ##STR56## and R² are as defined in (1); while R¹ is a ##STR57## group (wherein R³ is an alkyl group). It is particularly preferable that ##STR58## and R² are the preferable ones as defined in (1), while R¹ is a ##STR59## group (wherein R³ is an alkyl group).

In the compound represented by the general formula (IV), ##STR60## preferably represents a ##STR61## preferably represents a ##STR62## group; R¹ preferably represents a ##STR63## group (wherein R³ is an alkyl group); and R² preferably represents an ##STR64## (wherein R³ and R⁴ represent each an alkyl group) or ##STR65## group (wherein R⁶ is a hydrogen atom or an alkyl or alkoxy group). It is further preferable that ##STR66## R¹ and R² represent each the preferable group as cited above. When R² is a ##STR67## group, it is particularly preferable that R⁶ is an alkyl or alkoxy group, still preferably an alkyl group.

The compound of the general formula (I) may be synthesized by, for example, the following process A or B.

Process A: ##STR68##

Process B: ##STR69## wherein R¹, ##STR70##

R², m and n are as defined in the above general formula (I); and

X represents a halogen atom such as a bromine or iodine atom.

Either the process A or process B may be carried out by using a palladium catalyst such as dichlorobis(triphenylphosphine) palladium or palladium acetate optionally together with a solvent such as benzene, toluene, chlorobenzene or o-dichlorobenzene in the presence of, for example, diethylamine, triethylamine or tri-n-butylamine at a temperature of 0° to 150° C., preferably 20° to 100° C.

The azo compound of the present invention may be mixed with various liquid crystals to thereby give a liquid crystal composition.

As the liquid crystals, either nematic, cholesteric or smectic ones may be employed.

The nematic liquid crystals to be used in the present invention may be selected from those of a considerably wide range so long as they are present in a nematic state within a wide temperature range. These nematic liquid crystals may be converted into a cholesteric state by adding an optically active substance, which will be described hereinafter, thereto. Examples of the nematic liquid crystals include those shown in Table 1 as well as derivatives thereof.

                                      TABLE 1                                      __________________________________________________________________________     No.                                                                               Type      Example                                                           __________________________________________________________________________      1.                                                                               Cyclohexylcyclo- hexane                                                                   ##STR71##                                                         2.                                                                               Phenylcyclohexane                                                                         ##STR72##                                                         3.                                                                               Biphenyl                                                                                  ##STR73##                                                         4.                                                                               Terphenyl                                                                                 ##STR74##                                                         5.                                                                               Cyclohexylcyclo- hexanoate                                                                ##STR75##                                                         6.                                                                               Phenylcyclohexyl- carboxylate                                                             ##STR76##                                                         7.                                                                               Ester                                                                                     ##STR77##                                                         8.                                                                               Diester                                                                                   ##STR78##                                                                      ##STR79##                                                         9.                                                                               Biphenylcyclo- hexylcarboxylate                                                           ##STR80##                                                        10.                                                                               Biphenyl ester                                                                            ##STR81##                                                                      ##STR82##                                                           Thioester                                                                                 ##STR83##                                                           Schiff                                                                                    ##STR84##                                                                      ##STR85##                                                           Pyrimidine                                                                                ##STR86##                                                                      ##STR87##                                                                      ##STR88##                                                                      ##STR89##                                                           Dioxane                                                                                   ##STR90##                                                           Cyclohexyl methyl ether                                                                   ##STR91##                                                                      ##STR92##                                                           Cinnamonitrile                                                                            ##STR93##                                                           Ethane                                                                                    ##STR94##                                                                      ##STR95##                                                                      ##STR96##                                                           Dicyanophenyl ester                                                                       ##STR97##                                                                      ##STR98##                                                                      ##STR99##                                                                      ##STR100##                                                       __________________________________________________________________________

In the above Table 1, R' represents an alkyl or alkoxy group; R represents an alkyl group; and X' represents an alkyl, alkoxy, nitro or cyano group or a halogen atom.

Each liquid crystal in the Table 1 has a positive dielectric anisotropy. However known ester, azoxy, azo, Schiff, pyrimidine, diester or biphenyl ester type liquid crystals having a negative dielectric anisotropy may be mixed with a liquid crystal of a positive dielectric anisotropy to thereby give a liquid crystal composition of a positive dielectric anisotropy as the whole. Further liquid crystals of a negative dielectric anisotropy may be used as such by appropriately selecting the construction of a display and a driving system.

Either one of the liquid crystals shown in Table 1 or a mixture thereof may be used as the host liquid crystal substance of the liquid crystal composition according to the present invention. For example, liquid crystals ZLI-1132 or ZLI-1565 (mfd. by Merck Co., Inc.) or E-7 (mfd. by British Drug House) may be used therefor.

These nematic liquid crystals may be converted into a cholesteric state by adding an optically active substance described below.

Examples of the optically active substance to be used in the liquid crystal composition of the present invention include chiralnematic compounds obtained by introducing an optically active group, for example, 2-methylbutyl, 3-methylbutoxy, 3-methylpentyl, 3-methylpentoxy, 4-methylhexyl or 4-methylhextoxy group into a nematic liquid crystal. Further other optically active substances described in Japanese Patent Laid-Open No. 45546/1976, for example, alcohol derivatives such as 1-menthol or d-borneol; ketone derivatives such as d-camphor or 3-methylcyclohexane; carboxylic acid derivatives such as d-citronellic acid or 1-camphoric acid; aldehyde derivatives such as d-citronellal; alkene derivatives such as d-linonene; and other amine, amide and nitrile derivatives may be employed therefor.

Examples of the smectic liquid crystals to be used in the present invention include smectic A liquid crystals and smectic chiral C liquid crystals.

The content of azo compound in the liquid crystal composition of the present invention depends on the kinds of the liquid crystal or colors which the liquid crystal composition is going to show and is decided experimentally.

In the application of the liquid crystal composition of the present invention to a liquid crystal display device, a known liquid crystal display device may be used. Namely, a common display device comprises transparent electrodes of an arbitrary pattern located on two glass base plates, at least one of which is transparent. These glass plates are parallelly located in such a manner as that the electrodes face with each other via an appropriate spacer. The gap of the display device thus formed is determined by the spacer. From a practical viewpoint, a device gap of 1 to 100 μm, in particular, 2 to 50 μm is preferable.

The novel azo compound of the present invention shows a high dichroic ratio and a high solubility in liquid crystals. A liquid crystal composition containing said compound enables an excellent color display.

To further illustrate the present invention, and not by way of limitation, the following examples will be given.

Now an order parameter showing dichroism will be briefly described. The order parameter (S) of a dyestuff compound is experimentally determined by the following equation:

    (S)=(A∥-A⊥)/(A∥+2A⊥).

In the above equation, A∥ and A⊥ respectively represent the absorbances of the dyestuff compound for parallelly and vertically polarized lights to the alignment direction of the liquid crystal.

The order parameter (S) means the display contrast of a guest/host type liquid crystal device. The degree of residual tone in the white portion would decrease, which enables a light and distinct display of a clear contrast, as the value (S) theoretically approaches 1.

EXAMPLE 1 Synthesis of a compound of a formula ##STR101## 55 mg of cuprous iodide, 0.81 g of ethyl p-iodobenzoate and 0.88 g of triethylamine were added to 100 ml of o-dichlorobenzene. The resulting mixture was heated to 50° C. under a nitrogen gas stream. 30 mg of dichlorobis(triphenylphosphine) palladium and 23 mg of triphenylphosphine were added thereto and the obtained mixture was further stirred at 50° C. for three hours. The o-dichlorobenzene was distilled off under reduced pressure and the residue was purified by column chromatography by using silica gel as a carrier and chloroform as a solvent. Thus 0.70 g of the aimed compound was obtained (m.p.: 178°-179° C.).

The azo compound (dyestuff .compound) of the present invention thus obtained was added to a liquid crystal mixture ZLI-1565 (mfd. by Merck Co., Inc.) and heated to 70° C. or above. When the liquid crystals became an isotropic liquid, the mixture: was thoroughly stirred and then cooled by allowing to stand. After repeating this procedure, the above dyestuff compound was dissolved therein.

The liquid crystal composition of the present invention thus obtained was introduced into a device of a gap of 10 μm, which comprised transparent electrodes and two glass plates. On the surface of each glass plate to be contacted with said liquid crystals, a polyamide resin had been applied and cured, followed by homogeneously aligning by rubbing. When no voltage was applied to the device thus aligned, the abovementioned liquid crystals showed a homogeneous alignment and the dyestuff compound molecules also showed the same alignment as that of the host liquid crystals.

The absorption spectra of the guest/host type device thus obtained were determined by using parallelly and vertically polarized lights to the alignment direction of the liquid crystal molecules. Then the maximum absorption wavelength of the dyestuff compound for each polarized light was determined. At the determination of the absorbance of the dyestuff compound, the data were corrected depending on the absorbances of the host liquid crystals and glass plates and on the reflection loss of the device.

The order parameter (S) was calculated with the use of the A∥ and A⊥ to each polarized light according to the abovementioned equation:

    (S)=(A∥-A⊥)/(A∥+2A⊥)

Table 2-1 shows the results.

EXAMPLE 2 Synthesis of a compound of formula ##STR102## 60 mg of cuprous iodide, 0.53 g of a compound of formula: ##STR103## and 0.95 g of triethylamine were added to 100 ml of o-dichlorobenzene. The resulting mixture was heated to 50° C. under a nitrogen gas stream. Then 34 mg of dichlorobis(triphenylphosphine) palladium and 30 mg of triphenylphosphine were added thereto. The obtained mixture was further stirred at 50° C. for three hours. The reaction mixture was then treated in the same manner as the one described in Example 1. Thus 0.90 g of the aimed compound was obtained (m.p.: 126° to 127° C.).

By using the azo compound thus obtained, a guest/host device was formed in the same manner as the one described in Example 1. The maximum absorbance wavelength and order parameter (S) were calculated. Table 2-1, No. 2 shows the results.

EXAMPLE 3 Synthesis of a compound of formula ##STR104## 11 mg of cuprous iodide, 0.16 g of ethyl p-iodobenzoate, 0.31 g of tri-n-butylamine, 6 mg of dichlorobis(triphenylphosphine) palladium and 4 mg of triphenylphosphine were added to 70 ml of o-dichlorobenzene. The resulting mixture was stirred at 50° C. for three hours under a nitrogen gas stream. The reaction mixture was then treated in the same manner as the one described in Example 1. Thus 0.60 g of the aimed compound was obtained (m.p.: 200° to 201° C.).

By using the azo compound thus obtained, a guest/host device was formed in the same manner as the one described in Example 1. The maximum absorbance wavelength and order parameter (S) were calculated. Table 2-1, No. 31 shows the results.

EXAMPLE 4 Synthesis of a compound of formula ##STR105##

The procedure of Example 2 was repeated except that 1.0 g of the compound of formula: ##STR106## was substituted With 1.2 g of a compound of a formula: to thereby give 0.9 g of the aimed compound (m.p.: 196° to 197° C.).

By using the azo compound thus obtained, a guest/host device was formed in the same manner as the one described in Example 1. The maximum absorbance wavelength and order parameter (S) were calculated. Table 2-1, No. 43 shows the results.

EXAMPLE 5

The compounds shown in the following Tables 2-1 to 2-4 were prepared in the same manner as the one described in Example 1 or 2. The order parameter (S) and the maximum absorbance wavelength of each compound were determined. Tables 2-1 to 2-4 show the results.

    TABLE 2-1       ##STR107##               No. R.sup.1      ##STR108##       ##STR109##       ##STR110##       R.sup.2 (n.m.)λmax (S)parameterOrder       1      ##STR111##       ##STR112##       ##STR113##       ##STR114##       ##STR115##       539 0.82       2      ##STR116##       " " "       ##STR117##       539 0.82       3      ##STR118##       " "       ##STR119##       ##STR120##       543 0.80       4      ##STR121##       " " "       ##STR122##       540 0.81       5      ##STR123##       ##STR124##       ##STR125##       ##STR126##       ##STR127##       539 0.84       6      ##STR128##       "       ##STR129##       ##STR130##       ##STR131##       538 0.80       7      ##STR132##       " "       ##STR133##       ##STR134##       525 0.79       8      ##STR135##       "       ##STR136##       ##STR137##       ##STR138##       528 0.84       9      ##STR139##       ##STR140##       ##STR141##       ##STR142##       ##STR143##       518 0.80  10 (n)H.sub.15       C.sub.7      ##STR144##       ##STR145##       ##STR146##       ##STR147##       520 0.80       11      ##STR148##       ##STR149##       ##STR150##       ##STR151##       ##STR152##       533 0.79       12      ##STR153##       ##STR154##       ##STR155##       ##STR156##       ##STR157##       542 0.80       13      ##STR158##       " "       ##STR159##       ##STR160##       545 0.79       14      ##STR161##       " "       ##STR162##       ##STR163##       539 0.83       15      ##STR164##       ##STR165##       ##STR166##       ##STR167##       ##STR168##       539 0.83       16      ##STR169##       " " "       ##STR170##       539 0.83       17      ##STR171##       " " "       ##STR172##       544 0.82       18      ##STR173##       ##STR174##       " "       ##STR175##       545 0.81       19      ##STR176##       " " "       ##STR177##       540 0.80       20      ##STR178##       ##STR179##       ##STR180##       ##STR181##       ##STR182##       526 0.82       21      ##STR183##       " " "       ##STR184##       526 0.82       22      ##STR185##       " "       ##STR186##       ##STR187##       431 0.79       23      ##STR188##       " " "       ##STR189##       435 0.80       24      ##STR190##       " " " OC.sub.7 H.sub.15 (n) 450 0.78       25      ##STR191##       ##STR192##       ##STR193##       ##STR194##       ##STR195##       445 0.80  26 (n)H.sub.15       C.sub.7 " "      ##STR196##       ##STR197##       455 0.78       27      ##STR198##       " "       ##STR199##       ##STR200##       435 0.78       28      ##STR201##       "       ##STR202##       ##STR203##       ##STR204##       408 0.79       29      ##STR205##       "       ##STR206##       ##STR207##       OC.sub.7 H.sub.15      ##STR208##

                                      TABLE 2-2                                    __________________________________________________________________________      ##STR209##                                                                     No.                                                                               R.sup.1                                                                                         ##STR210##                                                                             ##STR211##                                                                             R.sup.2          (n.m.)λmax                                                                  (S)parameterOrde                                                              r                     __________________________________________________________________________     30                                                                                 ##STR212##                                                                                      ##STR213##                                                                             ##STR214##                                                                             ##STR215##      443 0.76                  31                                                                                 ##STR216##      "       "                                                                                       ##STR217##      450 0.77                  32                                                                                 ##STR218##      "       "                                                                                       ##STR219##      450 0.85                  33                                                                                 ##STR220##      "       "                                                                                       ##STR221##      444 0.83                  34                                                                                 ##STR222##                                                                                      ##STR223##                                                                             ##STR224##                                                                             ##STR225##      444 0.83                  35                                                                                 ##STR226##      "       "                                                                                       ##STR227##      444 0.83                  __________________________________________________________________________

    TABLE 2-3       ##STR228##                No. R.sup.1       ##STR229##       ##STR230##       ##STR231##       ##STR232##       R.sup.2 (n.m.)λmax (S)parameterOrder                 36       ##STR233##       ##STR234##       ##STR235##       ##STR236##       ##STR237##       ##STR238##       581 0.83       37      ##STR239##       " " " "       ##STR240##       582 0.85  38 (n)H.sub.11       C.sub.5 " " "      ##STR241##       ##STR242##       562 0.82       39      ##STR243##       "       ##STR244##       "       ##STR245##       ##STR246##       647 0.83       40      ##STR247##       ##STR248##       ##STR249##       ##STR250##       ##STR251##       NHC.sub.5 H.sub.11 (n) 652 0.81       41      ##STR252##       " " "       ##STR253##       C.sub.7 H.sub.15 (n) 650 0.81       42      ##STR254##       " "       ##STR255##       ##STR256##       ##STR257##       570 0.82

    TABLE 2-4       ##STR258##               No. R.sup.1      ##STR259##       ##STR260##       ##STR261##       R.sup.2 (n.m.)λmax (S)parameterOrder                43       ##STR262##       ##STR263##       ##STR264##       ##STR265##       ##STR266##       579 0.82       44      ##STR267##       " " "       ##STR268##       582 0.83       45      ##STR269##       " " "       ##STR270##       585 0.80       46      ##STR271##       " " "       ##STR272##       583 0.81       47      ##STR273##       ##STR274##       ##STR275##       ##STR276##       ##STR277##       583 0.81       48      ##STR278##       " " "       ##STR279##       579 0.83       49      ##STR280##       " " "       ##STR281##       579 0.81       50      ##STR282##       " " "       ##STR283##       579 0.81       51      ##STR284##       " " "       ##STR285##       580 0.83       52      ##STR286##       ##STR287##       ##STR288##       ##STR289##       ##STR290##       580 0.83       53      ##STR291##       ##STR292##       " "       ##STR293##       590 0.83       54      ##STR294##       " " "       ##STR295##       593 0.83       55      ##STR296##       " " " " 593 0.83       56      ##STR297##       " " "       ##STR298##       590 0.83       57      ##STR299##       ##STR300##       ##STR301##       ##STR302##       ##STR303##       585 0.80       58      ##STR304##       " " "       ##STR305##       580 0.82       59      ##STR306##       " " "       ##STR307##       582 0.82       60      ##STR308##       " "  "       ##STR309##       582 0.82       61      ##STR310##       " " "       ##STR311##       582 0.83  62 (n)H.sub.15       C.sub.7      ##STR312##       ##STR313##       ##STR314##       ##STR315##       575 0.80       63      ##STR316##       ##STR317##       " "       ##STR318##       582 0.83       64      ##STR319##       " "       ##STR320##       ##STR321##       540 0.83       65      ##STR322##       " "       ##STR323##       ##STR324##       539 0.84       66      ##STR325##       " "       ##STR326##       ##STR327##       590 0.84       67      ##STR328##       ##STR329##       ##STR330##       ##STR331##       ##STR332##       595 0.82       68      ##STR333##       " " "       ##STR334##       570 0.78       69      ##STR335##       " " "       ##STR336##       574 0.78       70      ##STR337##       " "       ##STR338##       ##STR339##       535 0.78       71      ##STR340##       " "       ##STR341##       ##STR342##       576 0.80       72      ##STR343##       ##STR344##       ##STR345##       ##STR346##       ##STR347##       578 0.80       73      ##STR348##       " " "       ##STR349##       576 0.80       74      ##STR350##       " " "       ##STR351##       581 0.80       75      ##STR352##       " "       ##STR353##       ##STR354##       542 0.81       76      ##STR355##       ##STR356##       ##STR357##       ##STR358##       ##STR359##       538 0.81       77      ##STR360##       ##STR361##       " "       ##STR362##       575 0.79       78      ##STR363##       ##STR364##       " "       ##STR365##       595 0.81       79      ##STR366##       ##STR367##       ##STR368##       ##STR369##       ##STR370##       545 0.79       80      ##STR371##       ##STR372##       ##STR373##       ##STR374##       ##STR375##       540 0.83       81      ##STR376##       " " "       ##STR377##       542 0.79

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. 

What is claimed is:
 1. An azo compound having a dichroism and being represented by the general formula (1): ##STR378## wherein R¹ represents a 1-16 carbon alkyl group or ##STR379## group (wherein R³ represents a 1-16 carbon alkyl group); ##STR380## represent each a ##STR381## group optionally substituted with a lower alkyl group or a halogen atom; R² represents a --OR³, ##STR382## (wherein R³ is as defined above and R⁴ represents a hydrogen atom or a 1-16 carbon alkyl group), ##STR383## (wherein R⁵ represents a hydrogen atom or a 1-16 carbon alkyl group and R⁶ represents a hydrogen atom or a 1-16 carbon alkyl or a 1-10 carbon alkoxy group), ##STR384## group; and a lower alkyl substituent in ##STR385## may bond to an alkyl group R³, R⁴ or R⁵ in ##STR386## of the R² group to thereby form a nitrogen-containing aliphatic ring.
 2. The azo compound of claim 1, wherein ##STR387## group optionally substituted with a lower alkyl group.
 3. The azo compound of claim 1, wherein ##STR388## group or a ##STR389## group optionally substituted with a lower alkyl group.
 4. The azo compound of claim 1, wherein ##STR390## group, a ##STR391## group or a ##STR392## group optionally substituted with a lower alkyl group.
 5. The azo compound of claim 1, wherein R¹ is a 1-16 carbon alkyl, ##STR393## group (wherein R³ is a 1-16 carbon alkyl group).
 6. The azo compound of claim 1, wherein R² is ##STR394## (wherein R³ and R⁴ represents each a 1-16 carbon alkyl group) or ##STR395## (wherein R⁶ represents a hydrogen atom or a 1-16 carbon alkyl or a 1-10 carbon alkoxy group).
 7. The azo compound of claim 1, wherein ##STR396## represents a ##STR397## group optionally substituted with a lower alkyl group; ##STR398## represents ##STR399## group or a ##STR400## group optionally substituted with an alkyl group; ##STR401## represents a ##STR402## group, a ##STR403## group optionally substituted with a lower alkyl group; R¹ represents an alkyl, ##STR404## group (wherein R³ represents a 1-16 carbon alkyl group); R² represents an ##STR405## (wherein R³ and R⁴ represent each a C₁₋₁₆ alkyl group) or ##STR406## group (wherein R⁶ represents a hydrogen atom or a 1-16 carbon alkyl or a 1-10 carbon alkoxy group).
 8. The azo compound of claim 7, wherein ##STR407## represents a ##STR408## represents a ##STR409## represents a ##STR410## group or a ##STR411## group optionally substituted with a lower alkyl group; R¹ represents a ##STR412## group (wherein R³ represents a 1-16 carbon alkyl group); R² represents an ##STR413## (wherein R³ and R⁴ represent each a C₁₋₁₆ alkyl group) or ##STR414## group (wherein R⁶ represents or a 1-16 carbon alkyl or a 1-10 carbon alkoxy group).
 9. The compound of claim 1, wherein ##STR415## represent each a ##STR416## group; R¹ represents a ##STR417## group (wherein R³ represents a 1-16 carbon alkyl group); and R² represents an ##STR418## group (wherein R³ and R⁴ represent each a 1-16 carbon group) or a ##STR419## group (wherein R⁶ represents a 1-16 carbon alkyl group).
 10. A liquid crystal composition comprising a liquid crystal and the azo compound of claim
 1. 11. The composition of claim 10, wherein the liquid crystal is nematic.
 12. The composition of claim 10, wherein the liquid crystal is cholesteric.
 13. The composition of claim 10, wherein the liquid crystal is smectic.
 14. An azo compound having a dichroism and being represented by the general formula (II): ##STR420## wherein R¹ represents a 1-16 carbon alkyl group or a ##STR421## group (wherein R³ represents an alkyl group); ##STR422## represent each a ##STR423## group optionally substituted with an alkyl group or halogen atom; R² represents an ##STR424## group (wherein R³ and R⁴ represent each a 1-16 carbon alkyl group) or a ##STR425## group (wherein R⁶ represents a hydrogen atom or a 1-16 carbon alkyl or a 1-10 carbon alkoxy group).
 15. A liquid crystal composition comprising a liquid crystal and the azo compound of claim
 14. 16. The composition of claim 15, wherein the liquid crystal is nematic.
 17. The composition of claim 15, wherein the liquid crystal is cholesteric.
 18. The composition of claim 15, wherein the liquid crystal is smectic. 